1. Field of the Invention
The present invention relates to a stop valve, more particularly to breathing system of a fuel tank for an internal combustion engine of an automobile, particularly to an improvement of a float type stop valve.
2. Prior Art
A breathing system is provided in a fuel tank for an internal combustion engine of an automobile for communicating with the atmosphere and a canister is provided in the breathing system for preventing evaporative emission being discharged toward the atmosphere.
If the breathing system is always open to the atmosphere, there is a likelihood that the fuel is leaked outside to bring about a big accident when the automobile (fuel tank) is largely inclined or forced to overturn. To prevent such inclination or overturning of the automobile, a stop valve is provided in the breathing system of the fuel tank for closing the breathing system.
The stop valve is generally used as a float type valve for closing the breathing system of the fuel tank by height of liquid level of the fuel on which the valve floats. In such a float type stop valve, when the automobile overturns, the float floats on the fuel so that the stop valve can not close the breathing system. Accordingly, the float is to be sunk using a weight or spring. When using the spring, a load applied to the float must be set considering the weight and buoyancy of the float, and hence there is a tendency that a weight type stop valve has been recently employed.
A prior art weight type stop valve will be now described with reference to FIG. 10 which is a cross-sectional view thereof.
A top wall of a fuel tank 1 is penetrated to provide a communication passage 2 constituting the breathing system of fuel.
A valve seat 3 and a valve body 4 for closing the valve seat 3 are provided in the communication passage 2. The valve body 4 is provided on a float 5. The float 5 floats on fuel in the fuel tank 1 and is movable vertically depending on surface of fuel, i.e. liquid level of the fuel in the communication passage 2.
A spherical weight 6 is provided under the float 5 for allowing the valve body 4 to weight or urge toward the valve seat 3 when placing on the float 5 when the automobile overturns. The weight 6 is normally placed on a pedestal 7.
The prior art stop valve operates as follows.
The fuel tank 1 communicates with atmosphere through the communication passage 2, a valve port of the valve seat 3 and a canister (not shown).
When the fuel tank 1 is largely inclined, the float 5 floats on the fuel so that the valve body 4 closes the valve seat. As a result, the fuel in the fuel tank 1 is prevented from being leaked outside through the breathing system.
When the automobile overturns, the fuel tank 1 is turned upside down so that the top wall of the fuel tank 1 is positioned at the bottom wall so that the float 5 is liable to float in the direction for the valve body 4 to open the valve seat 3. However, the weight 6 places on the float 5 and the valve body 4 closes the valve seat 3 by the weight of the weight 6. Accordingly, the fuel in the fuel tank 1 is prevented from being leaked outside through the breathing system.
However, there are following drawbacks in the prior art stop valve.
First, since the weight 6 swings in front and rear and left and right so that it strikes against the pedestal 7 or the communication passage 2. At this time, striking or shock sound is leaked outside as noise.
When the float 5 moves upward while it is inclined, there is a likelihood that the valve body 4 insufficiently closes the valve eat 3.